The present invention relates to a photodetector for use in read or write of an optical disc, a diffraction grating, an optical pickup, and an optical disc apparatus.
An optical pickup has been heretofore known that carries a two-wavelength multilaser thereon and uses a DPP method for generation of a tracking error signal and an astigmatic method for generation of a focusing error signal. In such an optical pickup, detection area patterns in a photodetector are formed in 3 rows×2 columns and a tracking error signal and a focusing error signal are generated in accordance with signals provided from the detection areas. See, for example, Patent Literature 1 (Japanese Patent Laid-open No. 2003-272218).
A technique is also known which simplifies the detection area patterns of 3 rows×2 columns described in Patent Literature 1 to reduce the cost of the photodetector. See, for example, Patent Literature 2 (Japanese Patent Laid-open No. 2005-85369).